Optical Characterization of Oligo(phenylene−ethynylene) Self-Assembled Monolayers on Gold

Richter, Lee J.; Yang, Clayton S.-C.; Wilson, P. T.; Hacker, Christina A.; Zee, Roger D. van; Stapleton, Joshua J.; Allara, David L.; Yao, Yuxing; Tour, James M.

doi:10.1021/jp0492366

Cited by 61 publications

(71 citation statements)

References 73 publications

(141 reference statements)

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“…Consequently, highly dilute solutions are required to fabricate true monolayers at the air–water interface. The UV/Vis spectrum of OPE2A in solution features one peak at 328 nm with two shoulders at 359 and 380 nm attributable to π–π* electronic transitions 6. 62…”

Section: Resultsmentioning

confidence: 99%

“…The UV/Vis spectrum of OPE2A in solution features one peak at 328 nm with two shoulders at 359 and 380 nm attributable to p-p* electronic transitions. [6,62] A preliminary investigation of the formation of Langmuir films of OPE2A involving both the concentration and the volume of the spreading solution concluded that only solutions of concentration 1 10 À5 m or lower yield reproducible isotherms. Figure 3 shows representative surface pressure versus area per molecule (p-A) isotherms of OPE2A on water (pH 5.9) and basic subphases (NaOH, pH 11.4).…”

Section: Resultsmentioning

confidence: 99%

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Controlling the Structural and Electrical Properties of Diacid Oligo(Phenylene Ethynylene) Langmuir–Blodgett Films

Ballesteros

Martı́n

Cortes

et al. 2013

Chemistry A European J

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The preparation, characterization and electrical properties of Langmuir-Blodgett (LB) films composed of a symmetrically substituted oligomeric phenylene ethynylene derivative, namely, 4,4'-[1,4-phenylenebis(ethyne-2,1-diyl)]dibenzoic acid (OPE2A), are described. Analysis of the surface pressure versus area per molecule isotherms and Brewster angle microscopy reveal that good-quality Langmuir (L) films can be formed both on pure water and a basic subphase. Monolayer L films were transferred onto solid substrates with a transfer ratio of unity to obtain LB films. Both L and LB films prepared on or from a pure water subphase show a red shift in the UV/Vis spectrum of about 14 nm, in contrast to L and LB films prepared from a basic subphase, which show a hypsochromic shift of 15 nm. This result, together with X-ray photoelectron spectroscopic and quartz crystal microbalance experiments, conclusively demonstrate formation of one-layer LB films in which OPE2A molecules are chemisorbed onto gold substrates and consequently -COO-Au junctions are formed. In LB films prepared on a basic subphase the other terminal acid group is also deprotonated and associates with an Na(+) counterion. In contrast, LB films prepared from a pure water subphase preserve the protonated acid group, and lateral H-bonds with neighbouring molecules give rise to a supramolecular structure. STM-based conductance studies revealed that films prepared from a basic subphase are more conductive than the analogous films prepared from pure water, and the electrical conductance of the deprotonated films also coincides more closely with single-molecule conductance measurements. This result was interpreted not only in terms of better electron transmission in -COO-Au molecular junctions, but also in terms of the presence of lateral H-bonds in the films formed from pure water, which lead to reduced conductance of the molecular junctions.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Controlling the Structural and Electrical Properties of Diacid Oligo(Phenylene Ethynylene) Langmuir–Blodgett Films

Ballesteros

Martı́n

Cortes

et al. 2013

Chemistry A European J

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“…SFG is a coherent process that detects the second-order nonlinear susceptibility of a material. Different components of the susceptibility tensor can be measured by using different polarization combinations of input and output laser beams (40)(41)(42)(43)(44)(45)(46)(47)(48)(49). As shown extensively in the literature (50)(51)(52)(53)(54)(55)(56), different susceptibility components can interfere with each other if some polarization combinations are adopted.…”

Section: Chiral Sfg Vibrational Spectra Of Adsorbed Fibrinogen Obtainmentioning

confidence: 99%

“…By assuming a molecular coordinate system for an antiparallel ␤-sheet as shown in Fig. 4, the SFG hyperpolarizability tensor elements (40,46,74,75) can be written as…”

Section: Direct Detection Of Strong Chiral Spectra From the Tachyplesmentioning

confidence: 99%

Detection of chiral sum frequency generation vibrational spectra of proteins and peptides at interfaces in situ

Wang

Chen

Clarke

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

186

245

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In this work, we demonstrate the feasibility to collect off-electronic resonance chiral sum frequency generation (SFG) vibrational spectra from interfacial proteins and peptides at the solid͞liquid interface in situ. It is difficult to directly detect a chiral SFG vibrational spectrum from interfacial fibrinogen molecules. By adopting an interference enhancement method, such a chiral SFG vibrational spectrum can be deduced from interference spectra between the normal achiral spectrum and the chiral spectrum. We found that the chiral SFG vibrational spectrum of interfacial fibrinogen was mainly contributed by the ␤-sheet structure. For a ␤-sheet peptide tachyplesin I, which may be quite ordered at the solid͞liquid interface, chiral SFG vibrational spectra can be collected directly. We believe that these chiral signals are mainly contributed by electric dipole contributions, which can dominate the chiroptical responses of uniaxial systems. For the first time, to our knowledge, this work indicates that the off-electronic resonance SFG technique is sensitive enough to collect chiral SFG vibrational spectra of interfacial proteins and peptides, providing more structural information to elucidate interfacial protein and peptide structures. chiral vibrational spectroscopy ͉ interfacial proteins and peptides U nderstanding chirality is important in biology, chemistry, and medicine. For example, chiral surfaces and interfaces are important in asymmetric chemical synthesis, chiral molecule separation, binding between chiral drugs and proteins, crystal growth, and the adsorption of proteins on biomedical material surfaces. Since the excellent work on chiroptical effects using second-harmonic generation (SHG) was presented by Hicks and coworkers (1-4) and Persoons and coworkers (5-7), extensive research has been performed to investigate such effects in oriented thin films or bulk media by using SHG and sum frequency generation (SFG) spectroscopic techniques (8-38). Many excellent experimental demonstrations and theoretical treatments on this topic have been published in the last decade or so. These studies indicate that more structural information about chiral materials can possibly be deduced by SHG and SFG studies. It has been demonstrated that the nonlinear chiral effect detected by nonlinear optical methods, such as SHG and SFG, can be several orders of magnitude larger than those detected by linear optical methods (refs. 8, 29, and 36 and references therein).Currently, several general models have been used to interpret the molecular mechanisms of second-order nonlinear chiral spectra (ref. 36 and references therein). Some experimental results can be interpreted by magnetic-dipole contributions and͞or interference between electric and magnetic-dipole contributions. For other experiments, the factors mentioned above cannot explain the very strong nonlinear chiral signal observed, and interpretations based on a pure electric-dipole contribution have been proposed. Recently, Shen and coworkers (10,17) demonstrated that chir...

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“…Tour et al [10] reported the first assembly of a nanocell with disordered arrays of molecules and Au islands, which exhibited reproducible switching behavior and memory effects at room temperature. Major efforts were also performed by Allara and co-workers at Pennsylvania State University, where gold clusters were used instead of discontinuous gold films in addition to extensive work on molecular self-assembly [114]- [119]. An extraordinary set of molecules for molecular circuits has been synthesized, assembled, and measured by Tour and co-workers at Rice [6], [16], [107], [108], [116], [120]- [143]; their suitable selection of molecules has been the actual drive for the development of molecular electronics.…”

Section: State Of the Art On Nanocellsmentioning

confidence: 99%

The Nanocell: A Chemically Assembled Molecular Electronic Circuit

Seminario

Tarigopula

2006

IEEE Sensors J.

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Computing is one of the most demanding applications of integrated circuits (IC). It requires the highest possible speed to process information. Higher speeds imply smaller circuits and, therefore, higher densities of integration. Thus, the most effective way to make faster circuits is by "scaling down," i.e., reducing the device size proportionally. However, under present technology, miniaturization is mainly constrained by the amount of heat dissipated as the number of devices increases per unit area and by the ability of lithographic tools to chisel smaller details on bulk substrates; these are technical constraints. However, there are physical or natural constraints which are practically material independent (speed of light, size of atoms, response of the electron, and Planck constant). Two main scenarios have been proposed for using molecules or small group of atoms (clusters) to build devices able to perform logical operations, bypassing, to some extent, problems undermining miniaturization or scaling-down processes for IC. One approach is the crossbar; a promising technology that uses directed self-assembly to make nanoarrays similar in shape to those already fabricated at larger scales by standard electronics. The other approach is the nanocell, which is a complementary design in the sense that it builds up (bottom-up) from single molecules into precise and complex structures that can be approached by standard lithography. This paper focuses on the description, advances, and possibilities of the nanocell approach, which takes advantage of the great skills developed by chemists to synthesize molecules with precise arrangements of atoms in a molecule. The nanocell concept does not require a deterministic assembly or deposition of molecules and clusters, thanks to the recently discovered programmability feature of molecules. Thus, in this paper, it is shown that the nanocell is a feasible concept for the development of electronics beyond deterministic lithographic approaches presently used in the fabrication of IC. The great importance and advantage of having molecular size computing devices is their ability to interact directly with external agents or molecules producing a sensor device already attached to a nanoprocessor that is able to strongly help in the stand-off detection of chemical and biological agents.

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Optical Characterization of Oligo(phenylene−ethynylene) Self-Assembled Monolayers on Gold

Cited by 61 publications

References 73 publications

Controlling the Structural and Electrical Properties of Diacid Oligo(Phenylene Ethynylene) Langmuir–Blodgett Films

Controlling the Structural and Electrical Properties of Diacid Oligo(Phenylene Ethynylene) Langmuir–Blodgett Films

Detection of chiral sum frequency generation vibrational spectra of proteins and peptides at interfaces in situ

The Nanocell: A Chemically Assembled Molecular Electronic Circuit

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